1. Field of the Invention
The present invention concerns a method to produce a curved coil, in particular a sub-coil of a gradient coil for a magnetic resonance apparatus as well as a winding plate for use in this method.
2. Description of the Prior Art
Large-area coils, for example sub-coils of a gradient coil of a magnetic resonance apparatus, are typically produced by introducing a wire of one or multiple millimeters in diameter into the groove of a winding plate. In the case of a gradient sub-coil, the groove path corresponds to a predetermined pattern that in turn is designed with regard to the magnetic fields to be generated by means of the sub-coils. After wrapping the conductor, which protrudes slightly from the groove in the wrapped position, a support plate is typically placed upon it that is firmly connected with the conductor by an adhesive layer. Because gradient coils are typically cylindrical coils, it is necessary to bend the sub-coils so produced on a corresponding radius, thus to curve them so that they can be integrated into the gradient coil that, as is generally known, is composed of multiple such sib-coils as well as additional magnetic field-generating or shielding components, after which the gradient coil together with all components is cast with an insulating material (advantageously a casting resin). This deforming ensues in a mechanical manner, meaning that the composite composed of conductor (typically a copper conductor) and insulating support plate, on which the conductor is overlaid over its entire surface, is deformed to the curvature of the sub-coil by means of a press or a roller. High shearing strains, which place high demands on the bonding and shear resistance of the employed adhesive as well as the support plate itself, thereby occur between the conductor and the support plate. These shearing strains become greater the tighter the arc radius. For some coils (such as, for example, a head coil as part of a magnetic resonance apparatus), very tight arc radii are formed. These high shearing strains can now lead to the situation that the adhesion locally detaches in the forming, or detaches at a later point in time due to the high strain load, which either makes the sub-coils unusable or leads to problems in the operation of the gradient coil after integration into the gradient coil has already occurred.